doc: move contribution guidelines to CONTRIBUTING.md (#44)

- fixes https://github.com/awesome-selfhosted/awesome-selfhosted-data/issues/40
- doc: ISSUE_TEMPLATE/other.md: cleanup
- doc: .github/PULL_REQUEST_TEMPLATE.md: fix link to addition template
- doc: LICENSE: fix license file header/auomatic license detection by Github
- doc: license: add link to summary of license terms
- doc: group authors and licenses sections

.github/ISSUE_TEMPLATE/other.md

@@ -4,5 +4,3 @@ about: Other issues.
 assignees: ''
 
 ---
-
-Please describe the issue below:

.github/PULL_REQUEST_TEMPLATE.md

@@ -6,7 +6,7 @@ To ensure your Pull Request is dealt with swiftly, please check the following (c
 - [ ] Submit one item per pull request. This eases reviewing and speeds up inclusion.
 - [ ] You have searched the repository for any relevant [issues](https://github.com/awesome-selfhosted/awesome-selfhosted-data/issues) or [PRs](https://github.com/awesome-selfhosted/awesome-selfhosted-data/pulls), including closed ones.
 - [ ] Any software you are adding is not already listed at any of [awesome-sysadmin](https://github.com/n1trux/awesome-sysadmin), [staticgen.com](https://www.staticgen.com/), [staticsitegenerators.net](https://staticsitegenerators.net/), [dbdb.io](https://dbdb.io/browse).
-- [ ] The file you are adding is formatted as described in [addition.md](https://github.com/awesome-selfhosted/awesome-selfhosted/blob/master/.github/ISSUE_TEMPLATE/addition.md).
+- [ ] The file you are adding is formatted as described in [addition.md](https://github.com/awesome-selfhosted/awesome-selfhosted-data/blob/master/.github/ISSUE_TEMPLATE/addition.md).
 - [ ] Comments and unused optional fields have been removed.
 - [ ] The file you are adding uses [kebab-case](https://en.wikipedia.org/wiki/Letter_case#Kebab_case) file naming, for example `my-awesome-software.yml`.
 - [ ] Values for `platform` are the main **server-side** requirements for the software. Don't include frameworks or specific dialects.